An adhering method for adhering a resin molded article to a rubber molded article by an adhesive is known as a process of integrally joining a resin molded element to a rubber molded element. However, the process using the adhesives not only complicates the process to cause a troublesome process-control with resulting in costly but also does not necessarily give a sufficient adhesive strength.
Meanwhile, a composite of a resin directly bonded to a rubber has been proposed. For example, Japanese Patent Application Laid-open No. 25682/1975 (JP-50-25682A) discloses a process for producing a rubber-plastic composite, which comprises rubbing a thermoplastic plastic component (e.g., a polyformaldehyde and an olefinic polymer) and a vulcanized rubber component (e.g., polybutadiene, nitrile) compatible with the thermoplastic plastic component with contacting each other to melt or fuse the surface of the plastic, and solidifying the melted surface of the resin with contacting the thermoplastic resin component and the vulcanized rubber component. However, in the process, since a configuration of the bonding site or position in the composite is restricted, it is difficult to produce a composite of a thermoplastic resin molded article and a rubber molded article, each having a complicated configuration on a bonding site, and to increase the productivity of the composite.
Regarding to a polyphenylene ether-rubber composite, Japanese Patent Application Laid-open No. 204260/1986 (JP-61-204260A) discloses a process for producing a composite, which comprises heating a polyphenylene ether-series resin which may have a styrenic polymer and/or an additive together with a synthetic rubber comprising SBR, BR, IR, IIR or the like in the presence of the vulcanizing system. The literature also discloses that a double bond-containing rubber vulcanizable by sulfur is suitable as the rubber component, and that a sulfur-containing compound is used as a vulcanization-activating agent. Further, a comparative example (Table 2) of the literature discloses an example using a rubber composition comprising E-SBR or BR as the rubber component and a peroxide-containing vulcanizing agent or a sulfur-containing vulcanizing agent.
With respect to an ABS resin-rubber composite, Japanese Patent Application Laid-open No. 301973/1993 (JP-5-301973A) discloses a process for producing a composite, which comprises laminating an ABS resin molded member and an unvulcanized-rubber sheet composed of a rubber component having a critical surface tension of 37 to 39 mN/m, and subsequently heating the laminated sheet for adhering integrally. Japanese Patent Application Laid-open No. 124803/1997 (JP-9-124803A) discloses a process for producing a composite member, which comprises heating an acrylonitrile-containing thermoplastic resin (e.g., AS resin, ABS resin) with an acrylonitrile-containing rubber with intimately contacting each other. However, these processes markedly restrict species of resins and rubbers for combination because the adhesion depends on a compatibility between the thermoplastic resin and the rubber, and therefore the practical applications are much limited.
Referring to a polyamide-rubber composite, Japanese Patent Application Laid-open No. 150439/1990 (JP-2-150439A), Japanese Patent Application Laid-open No. 133631/1991 (JP-3-133631A) and Japanese Patent Application Laid-open No. 138114/1991 (JP-3-138114A) disclose a process for producing a polyamide-rubber composite, which comprises vulcanizing or crosslinking a rubber component with contacting a polyamide-series resin in the presence of the vulcanizing agent, wherein the rubber component comprises a carboxyl group- or an acid anhydride group-containing rubber, a peroxide, a vulcanization-activating agent (e.g., ethylene glycol dimethacrylate, triallyl isocyanurate), and an alkoxysilane compound. In these documents, a polyamide-series resin containing the larger number of a terminal amino group than that of a terminal carboxyl group is used as an aliphatic polyamide-series resin. Since these processes utilize a reaction between an amino group and a carboxyl group or an acid anhydride group, a combination of species of resins and rubbers is markedly restricted, and therefore it is difficult to obtain a resin/rubber composite in a wide combination of the resin and the rubber.
Japanese Patent Application Laid-open No. 11013/1995 (JP-7-11013A) discloses a process for producing a composite member of a vulcanized rubber firmly bonded to a polyamide, which comprises vulcanizing or crosslinking a rubber compound composed of a peroxide-containing vulcanizing agent and a silane compound with contacting a polyamide molded article. The literature discloses that the rubber compound may contain, if necessary, a vulcanization-activating agent, and also discloses that, in a comparative example (Table 2), even if an EPDM rubber comprising a peroxide (perkadox 14/40) and butanediol dimethacrylate (BDMA) was vulcanized in contact with a polyamide-series resin, a bonding between the resin and the rubber was not effected. Therefore, the composite member is hardly produced without an expensive silane compound.
Japanese Patent Application Laid-open No. 156188/1996 (JP-8-156188A) discloses a process for producing a composite member, which comprises vulcanizing or crosslinking a carboxyl group- or an acid anhydride group-containing rubber member with contacting closely an epoxy group-containing resin member. However, since this process also uses a reaction between the epoxy group and the carboxyl group, a combined species of the resin and the rubber is markedly limited, and it is difficult to obtain composites widely.
Regarding a process for producing a polyester-rubber composite comprising a thermoplastic polyester as a hard component and a vulcanized rubber as a soft component, Japanese Patent Application Laid-open No. 304880/1995 (JP-7-304880A) discloses a use of a rubber component comprising a rubber, a peroxide vulcanizing agent, a di- or poly-functional maleimide, and, if necessary, a vulcanization-activating agent, and Japanese Patent Application Laid-open No. 166043/1995 (JP-7-166043A) proposes to use a rubber component comprising a rubber, a peroxide vulcanizing agent, a silane compound, and, if necessary, a vulcanization-activating agent. Further, concerning a composite film or sheet comprising a resin film and a rubber film, Japanese Patent Application Laid-open No. 58605/1998 (JP-10-58605A) discloses a process for producing a composite film by laminating a rubber film (e.g., silicone rubber, ethylene-propylene-series rubber) comprising a polyfunctional methacrylate as an adhesion-improving agent on a substrate film (e.g., a polyester film), and vulcanizing or crosslinking the laminate. However, such processes cause difficulty for bonding the polyester film to the rubber film with a high adhesive strength.
Thus, conventional techniques require trial and error investigation for obtaining a high adhesive strength in a combination of a thermoplastic resin and a rubber, and it is difficult to obtain generally or universally a combination of a thermoplastic resin with a rubber to firmly bond each other.
It is, therefore, an object of the present invention to provide a composite of a resin bonded directly to a rubber firmly without an adhesive in a wide extent of combinations of a resin and a rubber, and a process for producing the same.
Another object of the invention is to provide a composite excellent in an adhesive strength between a resin and a rubber, and a process for producing the same.